Heat transfer sheets

ABSTRACT

The heat transfer sheet according to this invention includes a substrate sheet and a dye carrier layer formed on one surface of said substrate sheet, and is characterized in that the dye included in the dye carrier layer is represented by the following general formula (I): ##STR1## wherein R 1  -R 4  and X each represent a substituent. According to this invention, it is possible to obtain image representations improved in terms of printing density and clearness as well as storability and resistance to discoloring and browning.

TECHNICAL FIELD

The present invention relates to a heat transfer sheet. Moreparticularly, the invention has for its object the provision of a heattransfer sheet capable of making image representations improved in termsof the density of developed colors, clearness and fastness properties,especially storability and resistance to discoloring and browning.

BACKGROUND ART

Various heat transfer techniques have so far been known in the art,including a sublimation transfer system wherein a sublimable dye iscarried on a substrate sheet as a recording material to form a heattransfer sheet, and that transfer sheet is then overlaid on animage-receiving material dyeable with such a sublimable dye, e.g. apolyester woven fabric to apply heat energy from the back surface of theheat transfer sheet, thereby transferring the sublimable dye onto theimage-receiving material.

More recently, it has been proposed to make various full-color images onpaper or plastic films, using the aforesaid sublimation type of heattransfer system. In this case, a printer's thermal head is used asheating means to apply very quick heating to transfer a number ofthree-, four- or multi-color dots onto an image-receiving material,thereby reconstructing a full-color image of the original image with,the multi-color dots. Because the coloring matter used is a dye, thethus formed image is very clear-cut and excels in transparency. Thusthat image is improved in terms of the reproducibility of the halftoneand gray scale, making it possible to form first-line imagerepresentations equivalent to those achieved by conventional offset orgravure printing and comparable to full-color photographs as well.

With the aforesaid heat transfer process, however, the most intractableproblems arise in connection with how clearly the resulting image candevelop colors, how long it will be well stored and how resistive itwill be to discoloring and browning.

In other words, it is required for fast recording that heat energy beapplied for as short a time as possible, say, on the order ofmilliseconds. Thus the sublimable dye and image-receiving material arenot well heated within such a short time, rendering it impossible tomake images of sufficient density.

In order to accommodate such fast recording, sublimable dyes havingsuperior sulimability have thus been developed. Since dyes excelling insublimability have generally a low molecular weight, however, they tendto migrate or bleed with time through image-receiving materials aftertransfer, offering storability problems such as making the resultingimages blurry or unclear or causing them to foul surrounding objects.

In order to avert such a problem, it has been proposed to use sublimabledyes having a relatively high molecular weight. However, their rate ofsublimation is too low for such high speed recording as mentioned aboveto make images of such sufficient density as aforesaid.

In addition, because the images are made from dyes, the resulting imagesare generally inferior in light fastness to pigmented images. Inaddition, they turn brown or discolor more prematurely than thepigmented images, when exposed to direct sunlight. Such light fastnessproblems may have been solved to some extent by adding UV absorbers orantioxidants to the dye-receiving layers of image-receiving materials.

However, the discoloring and browning problems arise by light other thandirect sunlight as well. For instance, discoloring or browning arelikely under indoor light or under such conditions as not directlyexposed to light, e.g. in albums, cases or books. These in-room orin-the-dark discoloring or browning problems can never be solved byusing general UV absorbers and antioxidants.

DISCLOSURE OF THE INVENTION

It is therefore an object of this invention to provide a heat transfersheet usable with a heat transfer system making use of sublimable dyes,which can give clear-cut images of sufficient density and allows them topossess superior fastness properties, especially having have excellentstorability and resistance to discoloring and browning.

The aforesaid object is achievable by the invention which will bedescribed hereinafter.

More specifically, the present invention provides a heat transfer sheetcomprising a substrate sheet and a dye carrier layer formed on onesurface of said substrate sheet, characterized in that the dye includedin said dye carrier layer is represented by the following generalformula (I): ##STR2## wherein;

R₁ and R₂ each stand for an identical or different substituted orunsubstituted alkyl, cycloalkyl, aralkyl or aryl group or an atom oratomic group forming a five- or six-membered ring together with X,provided that R₁ and R₂ may form together a five- or six-membered ringwhich may contain an oxygen or nitrogen atom;

R₃ and R₄ each represent an identical or different substituted orunsubstituted phenyl or naphthyl group or a heterocyclic groupcontaining at least one of oxygen, nitrogen and sulfur atoms, with theproviso that R₃ and R₄ cannot be phenyl groups at the same time;

X indicates a hydrogen atom, a halogen atom, a cyano group or a nitrogroup, or an alkyl, cycloalkyl, alkoxy, aryl, aralkyl, acylamino,sulfonylamino, ureido, carbamoyl, sulfamoyl, acyl or amino group whichmay have a substituent; and

n is an integer of 1 or 2.

By using a dye of specific structure, it is possible to provide a heattransfer sheet in which the dye easily migrates onto an image-receivingmaterial even by the application of heat energy within a very shorttime, thereby obtaining an image representation of high density andsuperior fastness properties, especially storability and resistance todiscoloring and browning.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will now be explained in greater detail withreference to its preferred embodiments.

The dyes used in this invention and represented by General Formula (I),for instance, may be easily produced by the alkaline coupling of animidazole compound expressed by the following general formula(3)--obtained by the reaction of an amidine derivative having thefollowing general formula (1) with an α-bromoacetyl derivative havingthe following general formula (2)--with an aniline compound expressed bythe following general formula (4) in the presence of an oxidizing agentsuch as silver chloride, ammonium persulfate or potassium ferricyanide.##STR3## wherein R₁ -R₄, X and n have the same meanings as alreadydefined.

The amidine derivatives of General Formula (I) may be synthiesized bygenerally available processes, e.g. those described in "J. Org. Chem.",27, 1255 (1962), "J. Org. Ghem. ", 28, 1812 (1963), and otherliterature. Also, the α-bromoacetyl derivatives of General Formula (2)may be easily synthesized by such a process as set forth in "Aust. J.Chem.", 19, 981 (1966) or "Org. Synth. Coll.", Vol II, 480, (1943).

Reference will now be made to preferable examples of various groups inGeneral Formula (I).

By way of example alone, mentioned as the alkyl group are methyl, ethyl,propyl, butyl, methoxyethyl, ethoxyethyl, hydroxyethyl, β-hydroxypropyl,chloroethyl, cyanomethyl and cyanoethyl groups; as the cycloalkyl groupa cyclohexyl; as aralkyl group benzyl and phenetyl groups; as aryl groupphenyl, tolyl, halogenophenyl and alkoxyphenyl groups; as theheterocyclic group furyl, thienyl, pyrrolyl, oxazolyl, isoxazolyl,thiazolyl, isothiazolyl, imidazolyl, pyrazolyl, triazolyl, pyranyl,pyridyl, pyridazinyl, pyrimidyl, pyrazinyl, indolyl, indazolyl,quinolyl, quinazolinyl and purinyl; as the halogen atom fluorine,bromine and iodine; as the alkoxyl group methoxy, ethoxy, propoxy andbutoxy groups; as the acylamino group acetylamino and benzoylaminogroups; as the sulfonylamino group methanesulfonylamino,ethanesulfonylamino and benzenesulfonylamino groups; as the ureido groupmethylureido, 1,3-dimethylureido and ethylureido groups; as thecarbamoyl group methylcarbamoyl, ethylcarbamoyl and phenylcarbamoyl; asthe sulfamoyl group methylsulfamoyl, ethylsulfamoyl and phenylsulfamoylgroups; as the acyl group acetyl, propanoyl and benzoyl groups; and asthe amino methylamino, ethylamino, propylamino, dimethylamino anddiethylamino groups.

When R₄ in General Formula (I) is a substituted or unsubstituted thienylgroup, images of superior light fastness are then obtainable. Moreover,when R₃ and R₄ are each an identical or different substituted orunsubstituted thienyl group, images having even more improved lightfastness are then attainable.

In the present invention, it is preferred that the dyes have a molecularweight of 400 or more. At a molecular weight less than 400, variousfastness properties such as storability and bleed resistance remaininsufficient.

When at least one of the groups R₁ -R₄ and X contains such polarsubstituents as halogen atoms or hydroxyl, cyano, acid amide,sulfonylamide and ester groups, the aforesaid fastness properties areeven more improved. Thus, the resulting heat transfer sheet will be freefrom dye migration (offset), and the like, even when stored in roll formover an extended period of time.

In addition, the heat transfer sheet comprising the aforesaid dye may beused with cyan and magenta sheets for heat transfer to make a full-colorimage. In this case, it is particularly desired that the half-width ofthe maximum absorption wavelength of the dye's absorption spectrum is130 nm or below in terms of reflection, since the development of cyanwith a very high purity takes place, making it possible to reproducefull colors more satisfactorily. It is noted that the term "half-width"refers to the width in nm of the absorption wavelength of a dye at 50%of the absorptivity at the maximum absorption wavelength of its visiblelight absorption spectrum.

By using the aforesaid dye in combination with such yellow and magentadyes as represented just below, it is possible to make full-color imageswith a particularly superior color reproducibility. ##STR4## Preferableexamples of the dyes well fit for this invention are set out in Table 1,in which the groups R₁₋₄, X and n in General Formula (I) are specifiedwith the dyes'molecular weights. It is noted that the groups which R₃and R₄ may have are defined in terms of position as follows. ##STR5##

                                      TABLE 1                                     __________________________________________________________________________    No.                                                                              R.sub.1                                                                           R.sub.2   R.sub.3    R.sub.4      X (n)    M.W.                        __________________________________________________________________________     1 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       --Ph       5-chloro-thienyl-2-                                                                        1-CH.sub.3 (1)                                                                         434.5                        2 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       --Ph       thienyl-2-   1-CH.sub.3 (1)                                                                         400.0                        3 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.4 OH                                                                    --Ph       thienyl-2-   1-CH.sub.3 (1)                                                                         416.0                        4 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       --Ph       3-acetyl-aminothienyl-2-                                                                   1-H      443.0                        5 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       --Ph       thienyl-2-   1-OC.sub.2 H.sub.5                                                                     430.0                        6 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       2-acetylamino-Ph                                                                         2-acetylamino-5-chloro-                                                                    1-CH.sub.3 (1)                                                                         548.0                                                   thienyl-3-                                         7 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       --Ph       thienyl-3-   1-CH.sub.3 (1)                                                                         400.0                        8 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.4 OH                                                                    2-methylcarbamoyl-Ph                                                                     5-cyano-thienyl-3-                                                                         1-CH.sub.3 (1)                                                                         498.0                        9 --C.sub.2 H.sub. 5                                                                --C.sub.2 H.sub.5                                                                       thienyl-3- thienyl-3-   1-CH.sub.3 (1)                                                                         407.0                       10 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       4-chloro-Ph                                                                              thienyl-2-   1-NHCOCH.sub.3                                                                         477.0                       11 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.4 Ph                                                                    4-cyano-Ph 5-cyano-thienyl-2-                                                                         1-CH.sub.3 (1)                                                                         526.0                       12 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.4 NHSO.sub.2 CH.sub.3                                                   thienyl-3- thienyl-3-   1-CH.sub.3 (1)                                                                         500.0                       13 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       --Ph       thienyl-2-   1,4-diCH.sub.3                                                                         414.0                       14 --C.sub.2 H.sub.5                                                                 --Ph      --Ph       5-chloro-thienyl-2-                                                                        --H (1)  468.5                       15 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       --Ph       thiazolyl-2- 1-CH.sub.3 (1)                                                                         401.0                       16 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       --Ph       pyrrolyl-2-  1-CH.sub.3 (1)                                                                         382.0                       17 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       --Ph       pyridyl-2-   1-CH.sub.3 (1)                                                                         395.0                       18 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       --Ph       furyl-2-     1-H (1)  370.0                       19 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       2-acetylamino-Ph                                                                         3-acetylamino-furyl-2-                                                                     1-CH.sub.3 (1)                                                                         498.0                       20 -- C.sub.2 H.sub.5                                                                --C.sub.2 H.sub.4 OH                                                                    furyl-2-   4-chloro-furyl-2-                                                                          1-CH.sub.3 (1)                                                                         424.0                       21 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       --Ph       furyl-3-     1-OC.sub.2 H.sub.5                                                                     414.0                       22 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       furyl-2-   2-propanoylamino-furyl-3-                                                                  1-H (1)  431.0                       23 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.4 CN                                                                    thienyl-2- 4-methyl-furyl-3-                                                                          1-CH.sub.3 (1)                                                                         429.0                       24 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       furyl-2-   4-cyano-tjoemu;-2-                                                                         1-CH.sub.3 (1)                                                                         415.0                       25 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.4 Cl                                                                    thienyl-2- 5-chloro-thienyl-2-                                                                        1-H (1)  461.0                       26 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.4 Ph                                                                    oxazolyl-2-                                                                              3-acetylamino-thienyl-2-                                                                   1-H (1)  510.0                       27 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       thiazolyl-2-                                                                             2-acetylamino-thienyl-3-                                                                   1-CH.sub.3 (1)                                                                         464.0                       28 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.4 OH                                                                    --Ph       pyrrolyl-2-  1-CH.sub.3 (1)                                                                         398.0                       29 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       furyl-2-   --Ph         1-CH.sub.3 (1)                                                                         384.0                       30 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       thienyl-2- --Ph         1-CH.sub.3 (1)                                                                         400.0                       31 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       thienyl-2- --Ph         1-OC.sub.2 H.sub.5                                                                     430.0                       32 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       5-chloro-thienyl-2-                                                                      --Ph         1-H (1)  420.0                       33 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       oxazolyl-5-                                                                              --Ph         1-CH.sub.3 (1)                                                                         385.0                       34 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       --Ph       oxazolyl-2-  1-OC.sub.2 H.sub.5                                                                     415.0                       35 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       --Ph       oxazolyl-4-  1-H (1)  371.0                       36 --C.sub.2 H.sub.5                                                                 --Ph      2-chloro-Ph                                                                              oxazolyl-2-  1-NHCOCH.sub.3                                                                         510.5                       37 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       --Ph       oxazolyl-4-  1-CH.sub.3 (1)                                                                         385.0                       38 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       2-acetylamino-Ph                                                                         oxazolyl-5-  1-OC.sub.2 H.sub.5                                                                     472.0                       39 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       4-methyl-Ph                                                                              isoxazolyl-3-                                                                              1-CH.sub.3 (1)                                                                         399.0                       40 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       --Ph       isoxazolyl-4-                                                                              1-CH.sub.3 (1)                                                                         385.0                       41 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.4 Ph                                                                    -- Ph      isoxazolyl-5-                                                                              1-OC.sub.2 H.sub.5                                                                     491.0                       42 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       --Ph       thiazolyl-2- 1-H (1)  387.0                       43 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.4 OH                                                                    --Ph       thiazolyl-2- 1-CH.sub.3 (1)                                                                         417.0                       44 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       --Ph       5-acetylamino-thiazolyl-2-                                                                 1-CH.sub.3 (1)                                                                         458.0                       45 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.4 OH                                                                    thiazolyl-4-                                                                             5-chloro-thiazolyl-2-                                                                      1-CH.sub.3 (1)                                                                         458.5                       46 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       thiazolyl-4-                                                                             5-chloro-thiazolyl-2-                                                                      1-NHCOCH.sub.3                                                                         485.5                       47 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       furyl-2-   4-cyano-thiazolyl-2-                                                                       1-CH.sub.3 (1)                                                                         416.0                       48 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       thienyl-2- 4-nitro-thiazolyl-2-                                                                       1-CH.sub.3 (1)                                                                         452.0                       49 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.4 Cl                                                                    --Ph       thiazolyl-4- 1-H (1)  421.5                       50 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       4-methoxycarbonyl-Ph                                                                     thiazolyl-5- 1-CH.sub.3 (1)                                                                         459.0                       51 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       4-hydroxy-Ph                                                                             2-chloro-thiazolyl-5-                                                                      1-CH.sub.3 (1)                                                                         451.5                       52 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub. 5                                                                      --Ph       isoxazolyl-5-                                                                              1-CH.sub.3 (1)                                                                         385.0                       53 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       --Ph       imidazolyl-5-                                                                              1-CH.sub.3 (1)                                                                         384.0                       54 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       thienyl-2- imidazolyl-5-                                                                              1-CH.sub.3 (1)                                                                         390.0                       55 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       imidazolyl-5-                                                                            --Ph         1-CH.sub.3 (1)                                                                         398.0                       56 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       --Ph       pyrazolyl-4- 1-CH.sub.3 (1)                                                                         384.0                       57 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       pyrazolyl-4-                                                                             pyrazolyl-4- 1-CH.sub.3 (1)                                                                         374.0                       58 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       pyrazolyl-4-                                                                             --Ph         1-CH.sub.3 (1)                                                                         384.0                       59 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       --Ph       furazyl-3-   1-CH.sub.3 (1)                                                                         386.0                       60 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       --Ph       pyrimidyl-5- 1-CH.sub.3 (1)                                                                         396.0                       61 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       --Ph       pyrimidyl-5- 1-CH.sub.3 (1)                                                                         396.0                       62 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       thienyl-2- thienyl-2-   1-CH.sub.3 (1)                                                                         406.4                       63 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       furyl-2-   thienyl-2-   1-CH.sub.3 (1)                                                                         390.4                       64 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       --Ph       thienyl-3-   1-NHCOCH.sub.3                                                                         443.4                       65 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       thienyl-2- thienyl-3-   1-CH.sub.3 (1)                                                                         406.4                       66 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       thienyl-2- thienyl-3-   1-OC.sub.2 H.sub.5                                                                     436.5                       67 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       thienyl-2- thienyl-3-   1-NHCOCH.sub.3                                                                         499.5                       68 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       thienyl-2- thienyl-3-   --H      392.4                       69 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       thienyl-2- thienyl-2-   1-NHCOCH.sub.3                                                                         449.5                       70 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.4 OH                                                                    thienyl-2- thienyl-2-   --H      408.4                       71 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.4 OCH.sub.3                                                             thienyl-2- thienyl-2-   --H      422.4                       72 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.4 OCOCH.sub.3                                                           thienyl-2- thienyl-2-   --H      450.4                       73 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.4 Ph                                                                    thienyl-2- thienyl-2-   --H      468.5                       74 --C.sub.2 H.sub.5                                                                 -- Ph     thienyl-2- thienyl-2-   --H      440.5                       75 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.4 CN                                                                    thienyl-2- thienyl-2-   --H      417.4                       76 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.4 Cl                                                                    thienyl-2- thienyl-2-   --H      426.8                       77 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.4 NHCOCH.sub.3                                                          thienyl-2- thienyl-2-   --H      449.4                       78 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.4 NHCH.sub.3                                                            pyridyl-2- thienyl-2-   --H      416.2                       79 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       thienyl-2- 5-bromo-thienyl-2-                                                                         --H      471.3                       80 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       thienyl-2- 5-cyano-thienyl-2-                                                                         --H      417.4                       81 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       benzothiazolyl-2-                                                                        thienyl-2-   --H      443.5                       82 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       indolyl-2- thienyl-2-   --H      424.4                       83 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       pyrazolyl-2-                                                                             thienyl-2-   1-CH.sub.3 (1)                                                                         376.3                       84 --C.sub.2 H.sub.5                                                                 --C.sub.2 H.sub.5                                                                       --Ph       thienyl-2-   --H      384.4                       __________________________________________________________________________

The heat transfer sheet of this invention is characterized by using sucha specific dye as aforesaid, and may otherwise be similar to heattransfer sheets so far known in the art.

The substrate sheet which is used for the present heat transfer sheetcontaining the aforesaid dye may be made of any known material havingsome heat resistance and strength. For instance, use may be made ofpaper, various forms of processed paper, polyester films, polystyrenefilms, polypropylene films, polysulfone films, polycarbonate films,aramid films, polyvinyl alcohol films, cellophane and so on, all havinga thickness of 0.5 to 50 μm, preferably 3-10 μm. Particular preferenceis given to the polyester films.

In the dye carrier layer formed on the surface of such a substrate sheetas aforesaid, the dye expressed by General Formula (I) is carried by anydesired binder resin.

For carrying the aforesaid dye, binder resins so far known in the artmay all be used. By way of example, use may preferably be made ofcellulosic resins such as ethylcellulose, hydroxyethylcellulose,ethylhydroxycellulose, hydroxypropylcellulose, methylcellulose,cellulose acetate and cellulose acetate butyrate; and vinylic resinssuch as polyvinyl alcohol, polyvinyl acetate, polyvinyl butyral,polyvinyl acetacetal, polyvinyl pyrrolidone and polyacrylamide. Amongothers and in consideration of heat resistance, dye migration and thelike, particular preference is given to polyvinyl butyral and polyvinylacetal.

While such a dye carrier layer is basically made of the aforesaidmaterial, it may additionally contain various additives such as thoseheretofore used, as occasion demands.

In order to form such a dye carrier layer, the aforesaid dye and binderresin may preferably be dissolved or dispersed in a suitable solvent,optionally together with other desired components, to prepare a coatingliquid or ink for forming the carrier layer. The coating liquid or inkis then coated on the aforesaid substrate sheet, followed by drying.

The thus formed carrier layer has a thickness of 0.2 to 5.0 μm,preferably about 0.4 μm to about 2.0 μm, with the aforesaid dye suitablyaccounting for 5 to 70% by weight, preferably 10-60% by weight of thecarrier layer.

While the heat transfer sheet according to this invention may be usefulas such for heat transfer, its dye carrier layer may additionally beprovided on the surface with an anti-tack or release layer. By theprovision of such a layer, it is possible to prevent the heat transfersheet from sticking to an associated image-receiving material duringheat transfer and so make images of much more improved densities byusing much higher heat transfer temperatures.

Considerable release effects may be obtained by mere deposition ofanti-tack inorganic powders. However, preference is given to a 0.01 to5-μm, preferably 0.05-2-μm thick release layer made of resins excellingin releasability, such as silicone, acrylic or fluorinated polymers.

It is understood that sufficient release effects are also obtainable,even when such inorganic powders or releasable polymers as aforesaid areincorporated in the dye carrier layer.

In addition, such heat transfer sheet may be provided on its back with aheat-resistant layer to prevent the heat of a thermal head from havingan adverse influence on it.

The image-receiving material which is used to form an image with such aheat transfer sheet as aforesaid may be made of any material with itsrecording surface being receptive with respect to the aforesaid dye.When it is made of dye receptivity-free materials such as paper, metals,glass or synthetic resins, it may be provided on at least one surfacewith a dye-receptive layer.

Image-receiving materials which may not be provided with anydye-receptive layer, for instance, may include fibers, woven fabrics,films, sheetings, and the like, made of polyolefinic resins such aspolypropylene; halogenated polymers such as polyvinyl chloride andpolyvinylidene chloride; vinylic polymers such as polyacrylic ester;polyester base resins such as polyethylene terephthalate andpolybutylene terephthalate; polystyrene base resins; polyamide baseresins; copolymeric resins such as those of olefins, e.g. ethylene orpropylene with other vinyl monomers; ionomers; cellulosic resins such ascellulose diacetate; and polycarbonates.

Particular preference is given to polyester sheets or films, orprocessed paper having a polyester layer. Even dye receptivity-freematerials inclusive of paper, metals and glass may be formed intoimage-receiving materials by coating a solution or dispersion of suchdye-receptive resins as aforesaid on their recording surfaces, followedby drying, or laminating films of those resins on their recordingsurfaces.

Even with the aforesaid dye-receptive image-receiving materials, betterresults are obtained if they are provided with a dye-receiving layer ofa resin better in dye receptivity than them, as is the case with paper.

The thus formed dye receiving-layer may be made of a material ormaterials, and may contain various additives as well, provided thatthey- offer no impediment to the achievement of the desired object.

Such a dye-receiving layer may have any desired thickness, but isgenerally in the range of 3 to 50 μm in thickness. Also, it may beformed into a continuous coat, or a discontinuous coat with resinemulsions or dispersion.

Constructed basically as aforesaid, such an image-receiving material mayserve well by itself. However, anti-tack inorganic powders may beincorporated in the aforesaid image-receiving material or itsdye-receiving layer, whereby more improved heat transfer can be carriedout even at elevated heat transfer temperatures, since the heat transfersheet is more unlikely to stick to the image-receiving material.Particularly preferable to this end is finely divided silica.

In place of or in combination with such inorganic powders as silicapowders, resins having increased releasability, e.g. such resins asaforesaid, may be added. Particularly preferable releasable polymers areset products of silicone compounds, e.g. set products comprising epoxyand amino-modified silicone oils. Such a releasant may preferablyaccount for about 0.5 to 30% by weight of the dye-receiving layer.

The image-receiving material used may have such inorganic powders asaforesaid deposited onto, or a layer of such a releasant as one havingincreased releasability formed on, the surface of its dye-receivinglayer, thereby enhancing the anti-tack effects.

Such a release layer produces sufficient effects at a thickness of about0.01 μm to about 5 μm, preventing the heat transfer sheet from stickingto the dye-receiving layer of the image-receiving material, whileimproving its dye receptivity.

Known heat energy applicator means may all be used for heat transferwith the aforesaid heat transfer sheet of this invention and such animage-receiving material as aforesaid. For instance, the desired objectis well attainable by applying a heat energy of about 5 mJ/mm² to about100 mJ/mm² a time controlled by recording equipment such as a thermalprinter (e.g. Video Printer VY-100 made by Hitachi, Ltd., Japan)

According to this invention as described above, the dye used toconstruct the present heat transfer sheet has superior heat migrationand allows the dye to be well received by the image-receiving materialand the image-receiving material to develop color, but does not bleedthrough the image-receiving material. This is because, in spite ofhaving a molecular weight much higher than that--a matter of 150 to250--of sublimable dyes used for conventional heat transfer sheets, thepresent dye has a specific structure and a substituent at a specificposition.

While the resulting image is made from the dye, yet it does not giverise to the discoloring and browning problems under indoor light or insuch states as not directly exposed to light, e.g. in albums, cases orbooks.

Thus the image representation made with the heat transfer sheet of thisinvention has much superior fastness properties, especially resistanceto migration and contamination, and such improved resistance todicoloring and browning, that even when stored over an extended periodof time, it will be most unlikely to fray, contaminate other objects andlose its clearness. All the problems incidental to the prior art canthus be solved.

The present invention will now be explained more illustratively withreference to Reference Examples, Examples and Comparative Examples,wherein unless otherwise stated, "parts" and "%" are given by weight.

REFERENCE EXAMPLE 1

Twenty (20.0) g of benzamidine hydrochloride dissolved in water wereneutralized with sodium hydroxide, and was thereafter extracted underagitation with dichloromethane. Ten (10.0) g of2-bromoacetyl-5-chlorothiophene were added to the resulting organic ordichloromethane phase, followed by 3-hour heating and reflux underagitation. After the completion of the reaction, crystals wereprecipitated by cooling and filtered out to obtain 8.5 g of2-phenyl-4-[2-(5-chlorothienyl)]-imidazole (with a melting point of 181°C. to 182° C. and in a 79% yield).

Ten (10.0) g of the aforesaid imidazole compound were dissolved in amixed ethyl acetate/ethanol solvent, and a total of 9.7 g of an aqueoussolution of soda carbonate and hydrochloric acid2-amino-5-diethylaminotoluene were successively added to the resultingsolution. After that, 21.6 g of ammonium persulfate were added dropwise.Following the completion of the dropwise addition, the reaction wasallowed to occur at room temperature for 1 hour to precipitate crystals,which were then filtered out. The obtained crystals were recrystallizedfrom ethyl acetate to obtain (in an 87% yield) a dye represented by thefollowing structural formula or specified under No. 1 in Table 1. Thedye had a melting point of 167° C. to 168° C. and showed a maximumabsorption wavelength of 650 nm (in ethyl acetate). ##STR6##

REFERENCE EXAMPLE 2

Other dyes mentioned in Table 1 were obtained by following theprocedures of Reference Example 1, provided that the starting materialscorresponding to said other dyes were used.

EXAMPLE 1

A dye carrier layer-forming ink composition comprising the followingcomponents was prepared and, then, coated on a 6-μm thick polyethyleneterephthalate subjected on its back surface to a heat-resistanttreatment to a dry coverage of 1.0 g/m². Subsequent drying gave a heattransfer sheet according to this invention.

    ______________________________________                                        Dye mentioned in Table 1                                                                              3 parts                                               Polyvinyl butyral resin                                                                               4.5 parts                                             Methyl ethyl ketone    46.25 parts                                            Toluene                46.25 parts                                            ______________________________________                                    

However, when the dye was insoluble in the aforesaid composition,suitable solvents such as DMF, dioxane and chloroform were used.

Next, a synthetic paper (Yupo FPG #150 made by Oji Yuka K.K.) serving asa substrate sheet was coated on one surface with a coating solutioncomposed of the following components to a dry coverage of 10.0 g/m².Subsequent 30-minute drying at 100° C. gave an image-receiving material.

    ______________________________________                                        Polyester resin (Vylon 200 made by Toyobo                                                                11.5 parts                                         Co., Ltd., Japan)                                                             Vinyl chloride/vinyl acetate copolymer                                                                   5.0 parts                                          (VYHH made by UCC)                                                            Amino-modified silicone (KF-393 made                                                                     1.2 parts                                          by The Shin-Etsu Chemical Co., Ltd.,                                          Japan)                                                                        Epoxy-modified silicone (KF-22-343 made                                                                  1.2 parts                                          by The Shin-Etsu Chemical Co., Ltd.)                                          Methyl ethyl ketone/toluene/cyclohexanone                                                               102.0 parts                                         at a weight ratio of 4:4:2                                                    ______________________________________                                    

The heat transfer sheet of this invention was overlaid on the aforesaidimage-receiving material, while the former's dye carrier layer was inopposition to the latter's dye-receiving layer. Recording was performedfrom the back surface of the heat transfer sheet at a head applicationvoltage of 10 V for a printing time of 4.0 msec. The results arereported in Table 2.

                  TABLE 2                                                         ______________________________________                                        Density of   Storability                                                             Developed Resistance to Light Color                                    Dyes   colors    heat migration                                                                              fastness                                                                            tones                                    ______________________________________                                         1     2.50      ◯ ◯                                                                       blue                                      2     2.57      ◯ ◯                                                                       blue                                      3     2.21      ◯ ◯                                                                       blue                                      4     2.49      ◯ ◯                                                                       blue                                      5     2.45      ◯ ◯                                                                       blue                                      6     2.27      ◯ ◯                                                                       blue                                      7     2.57      ◯ ◯                                                                       blue                                      8     2.14      ◯ ◯                                                                       blue                                      9     2.54      ◯ ⊚                                                                    blue                                     10     2.46      ◯ ◯                                                                       blue                                     11     2.22      ◯ ◯                                                                       blue                                     12     2.16      ◯ ⊚                                                                    blue                                     13     2.48      ◯ ◯                                                                       blue                                     14     2.25      ◯ ◯                                                                       blue                                     15     2.38      ◯ ◯                                                                       blue                                     16     2.61      ◯ ◯                                                                       blue                                     17     2.62      ◯ ◯                                                                       blue                                     18     2.56      ◯ Δ                                                                             blue                                     19     2.21      ◯ Δ                                                                             blue                                     20     2.17      ◯ Δ                                                                             blue                                     21     2.46      ◯ Δ                                                                             blue                                     22     2.47      ◯ Δ                                                                             blue                                     23     2.43      ◯ Δ                                                                             blue                                     24     2.48      ◯ Δ                                                                             blue                                     25     2.44      ◯ ⊚                                                                    blue                                     26     2.34      ◯ ◯                                                                       blue                                     27     2.34      ◯ ◯                                                                       blue                                     28     2.19      ◯ Δ                                                                             blue                                     29     2.49      ◯ Δ                                                                             blue                                     30     2.49      ◯ ◯                                                                       blue                                     31     2.32      ◯ ◯                                                                       blue                                     32     2.37      ◯ ◯                                                                       blue                                     33     2.47      ◯ Δ                                                                             blue                                     34     2.45      ◯ Δ                                                                             blue                                     35     2.66      ◯ Δ                                                                             blue                                     36     2.23      ◯ Δ                                                                             blue                                     37     2.58      ◯ ◯                                                                       blue                                     38     2.27      ◯ ◯                                                                       blue                                     39     2.63      ◯ ◯                                                                       blue                                     40     2.51      ◯ ◯                                                                       blue                                     41     2.26      ◯ ◯                                                                       blue                                     42     2.57      ◯ ◯                                                                       blue                                     43     2.18      ◯ ◯                                                                       blue                                     44     2.30      ◯ ◯                                                                       blue                                     45     2.08      ◯ ◯                                                                       blue                                     46     2.32      ◯ ◯                                                                       blue                                     47     2.56      ◯ Δ                                                                             blue                                     48     2.21      ◯ ◯                                                                       blue                                     49     2.56      ◯ ◯                                                                       blue                                     50     2.33      ◯ ◯                                                                       blue                                     51     2.06      ◯ ◯                                                                       blue                                     52     2.61      ◯ ◯                                                                       blue                                     53     2.50      ◯ ◯                                                                       blue                                     54     2.43      ◯ ◯                                                                       blue                                     55     2.56      ◯ ◯                                                                       blue                                     56     2.44      ◯ ◯                                                                       blue                                     57     2.55      ◯ ◯                                                                       blue                                     58     2.55      ◯ Δ                                                                             blue                                     59     2.46      ◯ Δ                                                                             blue                                     60     2.61      ◯ Δ                                                                             blue                                     61     2.58      ◯ Δ                                                                             blue                                     62     2.48      ◯ ⊚                                                                    blue                                     63     2.83      ◯ Δ                                                                             blue                                     64     2.57      ◯ ◯                                                                       blue                                     65     2.73      ◯ ⊚                                                                    blue                                     66     2.69      ◯ ⊚                                                                    blue                                     67     2.59      ◯ ⊚                                                                    blue                                     68     2.65      ◯ ⊚                                                                    blue                                     69     2.95      ◯ ⊚                                                                    blue                                     70     2.34      ◯ ⊚                                                                    blue                                     71     2.43      ◯ ⊚                                                                    blue                                     72     2.47      ◯ ⊚                                                                    blue                                     73     2.39      ◯ ⊚                                                                    blue                                     74     2.52      ◯ ⊚                                                                    blue                                     75     2.55      ◯ ⊚                                                                    blue                                     76     2.34      ◯ ⊚                                                                    blue                                     77     2.09      ◯ ⊚                                                                    blue                                     78     2.22      ◯ ⊚                                                                    blue                                     79     2.44      ◯ ⊚                                                                    blue                                     80     2.36      ◯ ⊚                                                                    blue                                     81     2.37      ◯ ⊚                                                                    blue                                     82     2.54      ◯ ⊚                                                                    blue                                     83     2.55      ◯ ⊚                                                                    blue                                     84     2.43      ◯ ◯                                                                       blue                                     ______________________________________                                    

COMPARATIVE EXAMPLES 1-5

The procedures of Example 1 were followed with the exception that thedyes set out in Table 3 were used. The results are reported in Table 3.

                  TABLE 3                                                         ______________________________________                                                   Density of                                                         Comparative                                                                              Developed Storability                                              Examples   colors    A        B    Color tone                                 ______________________________________                                        1          0.99      X        Δ                                                                            Blue                                       2          1.16      Δ  Δ                                                                            Blue                                       3          2.07      X        Δ                                                                            Blue                                       4          1.12      Δ  Δ                                                                            Blue                                       5          1.02      X        Δ                                                                            Indigo                                     ______________________________________                                         A: Resistance to heat migration                                               B: Light fastness                                                             Comparative Ex.                                                               1: C.I. Disperse Blue 14                                                      2: C.I. Disperse Blue 134                                                     3: C.I. Solvent Blue 63                                                       4: C.I. Disperse Blue 26                                                      5: C.I. Disperse Violet 43                                                    It is noted that the aforesaid density of developed colors was obtained       with Densitometer RD918 made by Macbeth Co., Ltd. U.S.A.).               

The resistance to heat migration was measured by allowing the image tostand in a 70° C. atmosphere for 48 hours. A double circle indicatesthat the image suffered no change in sharpness and white paper was notcolored even when the image was rubbed on its surface with it; a circleindicates that the image suffered a slight change in sharpness and whitepaper was slightly colored; a triangle indicates that the image lostsharpness and white paper was colored; and a cross indicates that theimage became blurry and white paper was badly colored.

The light fastness was determined by allowing the image to be irradiatedwith light from an xenon light source until a third grade piece of ablue scale was colored. A double circle indicates that no discolorationtook place at all; a circle indicates that slight discoloration tookplace; and a triangle indicates that serious discoloration took place.

INDUSTRIAL APPLICABILITY

The heat transfer sheets according to this invention can find wideapplications in printing and image-making with heat transfer systems.

What is claimed is:
 1. A heat transfer sheet comprising:a substratesheet; and a dye carrier layer formed on one surface of said substratesheet, the dye included in said dye carrier layer comprising a dyerepresented by the following general formula (I): ##STR7## wherein: R₁and R₂ each stand for an identical or different substituted orunsubstituted alkyl, cycloalkyl, aralkyl or aryl group or an atom oratomic group forming a five- or six-membered ring together with X,provided that R₁ and R₂ may form together a five- or six-membered ringwhich may contain an oxygen or nitrogen atom;R₃ and R₄ each represent anidentical or different substituted or unsubstituted phenyl or naphthylgroup or a heterocyclic group containing at least one of oxygen,nitrogen and sulfur atoms, with the proviso that R₃ and R₄ cannot bephenyl groups at the same time; X indicates a hydrogen atom, a halogenatom, a cyano group or a nitro group, or an alkyl, cycloalkyl, alkoxy,aryl, aralkyl, acylamin-o, sulfonylamino, ureido, carbamoyl, sulfamoyl,acyl or amino group which may have a substituent; and n is an integer of1 or
 2. 2. A heat transfer sheet as claimed in claim 1, wherein R₄ is asubstituted or unsubstituted thienyl group.
 3. A heat transfer sheet asclaimed in claim 1, wherein R₃ and R₄ are identical or different,substituted or unsubstituted thienyl groups.
 4. A heat transfer sheet asclaimed in claim 1, wherein the dye has a molecular weight of 400 ormore.
 5. A heat transfer sheet as claimed in claim 1, wherein at leastone of the groups R₁ -R₄ and X contains a polar substituent.
 6. A heattransfer sheet as claimed in claim 1, wherein the half-width of themaximum absorption wavelength of the dye in a visible light absorptionspectrum is 130 nm or less in terms of reflection.